Invent your own chess piece!

The berserker. Replaces one random pawn in each army. Moves forward and promotes like a pawn, but does not not capture like a pawn. Instead it can capture a piece (but not a pawn!) by moving directly forward onto the piece-occupied square. In effect, pawns can blockade the berserker, but pieces cannot. The berserker is immune to en passant capture, but not to standard pawn capture, or any other type of standard capture.

I give you the Templar. It moves in a dual kind of way to a Knight. Placed near the center of the board, there are 8 squares it can move to, like a Knight, but forming the pattern pictured below (imagine the Templar placed on the red square; its available squares to move to and/or attack are in blue):

The Templar moves to any of the outer 4 blue squares in this picture by 'jumping' over the adjacent square that it can't move to.

Note that Templars come in light and dark varieties, like Bishops. Templar Chess is played on a 10x10 board, labeled a1 through j10 in algebraic notation, with a White Rook on a1, Knight on b1, Bishop on c1, Templar on d1, Queen on e1, King on f1, Templar on g1, Bishop on h1, Knight on i1, and Rook on j1. 10 pawns occupy the b rank, and the setup for Black is the mirror opposite of this, as in standard chess. (I chose this setup so that the fianchetto maneuver is still possible.)

A Templar is less mobile than a Knight, but as compensation it has a somewhat more flexible looking attack pattern, and performs better on the edge of the board or in a corner. Overall I'm not sure if it should be worth more or less than a Knight, or equal.

The Bird.

Each player starts with one Bird replacing his c-pawn. The Bird, on its first move, can either move two spaced forward (like a pawn) and convert itself straight back into a pawn, or it can move exactly five spaces diagonally. The Bird captures the same way that it moves, exactly five spaces diagonally - not four, not three. The Bird can be captured by any piece other than another Bird or a Pawn. If a Bird tries to capture another Bird, both Birds are removed from the board (This is called a "midair collision").

oh yeah, one of the fish called a boat a "butt"

Yeah,it was funny.

"I know what it's called. It's, it's, it's, it's called a butt!" later... *gasps*! "He touched the butt

Suicide bomber:

Moves, captures like a pawn. When it reaches the 8th/ 1st rank, instead of promoting it destroys all pieces on that rank.

It would probably be worth less than a pawn, since it's pretty useless in endgames.

You can also promote to a king and have 2 lives

Does your opponent know which one of your pawns is the chameleon pawn?

Dunno. Also the tear gasser. Renders all pieces on diagonals that it occupies for 5 turns

I just thought of an interesting way that one side could win if he has a huge material advantage, and the other side has a suicide bomber:

trolololol if that happened to anyone after the suicide bomber became a legitimate piece. Also each side gets two tear gassers and they move like knights and start on c3 and a3

This is a chess variant I came up with.
This variant (and the piece itself) is called the 'Disguised Pawn'. Each player has one of them.
This piece is actually disguised as a pawn and hides among the others. Each player, before the game, puts something (like a piece of scotch tape or something) at the bottom of a selected pawn and places it to any of the pawns' original place (2nd and 7th rank) at wish.
Of course, neither player knows which pawn is the disguised one on the other side.
It moves like a Queen at will, and it does not check the enemy King immediately if the enemy King is any of its attacked square, but does so if the player reveals the pawn's "true nature".
The players can reveal their own disguised pawns by simply moving them a way a normal pawn couldn't, or declare check (or even checkmate), if it's possible using the piece's queen moves.
For example: King is attacked and can't move, the disguised pawn is three squares away diagonally; the player reveals the pawn, and gives mate.
If the disguised pawn is promoted, it simply turns into a queen (the player does not have to admit that the pawn was the disguised pawn, but can so, if he wants to).
This last rule seems funny, but imagine if you have two past-pawns (one of them is the disguised one and the other is a normal one), and your opponent runs after the wrong one.
Me and some friends have played this version quite a few times; it makes really interesting endgames if the players don't get too greedy and reveal their disguised pawns early in the game to capture a minor piece.

The disguised pawn idea sounds interesting. I suppose that it probably wouldn't be a good idea to put your disguised pawn on the d file or e file, since those pawns often get traded off, and if your opponent sees that you're really reluctant to trade off one of your pawns, he'll probably guess that it is the disguised pawn.

A piece called the warrior.It moves to any square on the board but can't capture.

Yes, indeed, but after playing a few games with them, you can place them on the d or e file, and just watch your opponent's reaction when you suddenly have a queen in the center forking 3 pieces.
Your latter point is interesting, but that's actually the whole point of the game.
You can simply defend a normal pawn and act like you're worried about it, tricking your opponent into believing that's the disguised pawn, luring all of his forces to a specific area of the board, while preparing for a counter attack on the undefended side with the actual disguised pawn.

So it doesn't actually do anything except blocking checks? The name seems weird. Why isn't it the blocker, or defender, then?

The roadblock. It's a small cube. Before the game, players roll a die to see who gets possession of it. Winner gets it. Then, still before the game, the player places it anywhere on the board (except on squares occupied by pieces). The opponents pieces can't go through it, check through it, or capture it, or give mate through it,

but it can't do anything but act like a roadblock (so it can't capture). Also, your own pieces can only go on top of it, even when they want to go through it, but can give check(mate) through it. Actually it can only be captured by a promoted pawn piece. It is worth 123456789 points and the side with the roadblock loses if it's captured.